Merge pull request #22974 from Evalle/DOC-22953

ISSUE-22953: add missing information about etcd images

Author: k8s-ci-robot

content/en/docs/setup/production-environment/tools/kubeadm/setup-ha-etcd-with-kubeadm.md

@@ -29,6 +29,9 @@ when using kubeadm to set up a kubernetes cluster.
   document assumes these default ports. However, they are configurable through
   the kubeadm config file.
 * Each host must [have docker, kubelet, and kubeadm installed](/docs/setup/production-environment/tools/kubeadm/install-kubeadm/).
+* Each host should have access to the Kubernetes container image registry (`k8s.gcr.io`) or list/pull the required etcd image using
+`kubeadm config images list/pull`. This guide will setup etcd instances as
+[static pods](https://kubernetes.io/docs/tasks/configure-pod-container/static-pod/) managed by a kubelet.
 * Some infrastructure to copy files between hosts. For example `ssh` and `scp`
   can satisfy this requirement.